1. Field of the Invention
This invention relates to an agent for water treatment which is effective in preventing scale formation, and more particularly to an agent for water treatment which contains a water-soluble polymer derived from a water-soluble monomer component exhibiting fluorescence and which is excellent in resistance of the polymer to gelation (hereinafter referred to as "gelation resistance").
2. Description of the Related Art
An organic compound such as water-soluble polymer has been widely used as an agent for preventing scale formation and an inhibitor against metal corrosion to prevent scale formation and corrosion in an aqueous system such as boiler water and cooling water. In the case of being used for preventing scale formation or inhibiting metal corrosion, the water-soluble polymer cannot exhibit a sufficient prevention or inhibiting effect unless the concentration of polymer in water is kept within a predetermined range. Accordingly, in practice, it is verified whether the polymer maintains its concentration at an optimum operation value by measuring the concentration of polymer for use in water treatment in an aqueous system while circulating boiler water or cooling water.
As a method for measuring the concentration of polymer for use in water treatment, there have been known colorimetric method, nephelometric method, lithium tracer method, and fluorescent tracer method. These methods have suffered the following problems. In colorimetric method and nephelometric method, normally, a great deal of time is required for manual measurement. Even if the measurement is conducted automatically, time required for such automatic measurement cannot be shortened either.
On the other hand, lithium tracer method and fluorescent tracer method are not a direct measurement method of directly measuring the concentration of polymer, but an indirect measurement method. Accordingly, in the case where a consumption amount of polymer is greatly changed due to an exceeded concentration of water which is to be treated and formation of scale, these indirect measurement methods fail to grasp the consumption amount of polymer accurately.
Recently, there have been proposed methods of measuring the concentration of polymer in a simplified, speedy and accurate manner by directly introducing a compound capable of absorbing ultra-violet radiation (European Laid-open Patent Publication No. EP647596) or a fluorescent substance (Japanese Laid-open Patent Publication No. 5-163591) into a polymer for water treatment. Introducing a compound capable of absorbing ultra-violet radiation and a fluorescent substance (hereinafter referred to as a "labeled compound") into a polymer is performed utilizing a polymer reaction of reacting a functional group in the polymer with a functional group in the labeled compound. However, in the case of polymer reaction, the reaction rate of the functional group in the polymer is low, and it is difficult to introduce the labeled compound into the polymer at a specified amount. Hence, the concentration of polymer in water to be treated cannot be accurately measured. Further, kinds of labeled compounds which have a functional group reactable with a functional group in polymer are few, and the combination of these polymers and labeled compounds are also limited.
There has also been proposed a method of introducing a labeled compound into a polymer by adding for copolymerization a labeled compound having an unsaturated double bond into a reaction system in obtaining a polymer for use in water treatment. However, all labeled compound monomers obtainable at the present have lipophilicity. Accordingly, an additional process of removing a solvent by distillation is required after copolymerization in an organic solution, which not only makes the process of obtaining water-soluble polymer for use in water treatment cumbersome but also is not advantageous in the aspect of environment, preventing a fire, cost performance and saving natural resources. Moreover, the introducing rate of labeled compound monomers is low, for which an improvement has been demanded.